A height adjustment relative to the undercarriage must be possible for the drive unit in vehicles of the mentioned type, in order to guarantee at a ground unevenness that the ground contact of the drive or steering wheel is maintained with a sufficient pressure. Drives have already been designed in which the drive or steering wheel is supported on a movable bracket and is spring-suspended to an extent corresponding with the necessary height adjustment. Three such known devices are illustrated in FIGS. 1 to 3. All have the disadvantage that a vertical and position-neutral guiding is not guaranteed for the drive or steering wheel in the area of the height adjustment, which guiding, however, is absolutely necessary for good driving behavior. A further disadvantage of the embodiments according to FIGS. 1 and 2 is the relatively great physical height, and furthermore the relationship Y:Y'&gt;1 must be viewed as very unfavorable (Y identifying the distance of the bracket pivot point from the ground and Y' identifying the radius of the drive or steering wheel). With its shorter physical height and a relationship of Y:Y'=1, the embodiment according to FIG. 3 does not have these disadvantages, but that suspension system, which must also participate in the steering movement, is overregulated.
An object of the invention is to eliminate these disadvantages of known designs by providing a drive unit of the mentioned type which is constructed so that its guide makes possible in the range of the movement necessary for the height adjustment a most extensive vertical and position-neutral shifting, during which any kind of canting and thus wedging or clamping is impossible, and so that the entire unit has a relatively small physical height.